Thermoplastic resin films, in particular, biaxially oriented polyester films are excellent in mechanical property, electric property, dimension stability, heat resistance, transparency, chemical resistance and other properties; thus, the films are widely used as a base film for many materials such as magnetic recording materials, wrapping materials, electrically insulating materials, various photographic materials, photosensitive materials, thermosensitive materials, and graphic art materials. In particular, the use frequency thereof has been rising as various optical films, a typical example thereof being a displaying member concerned with display, in connection with the advance of IT technique in recent years.
In particular, polyester films are used as the base film of hard coat films, antireflective films, plasma lens films, lenticular lens films, optical diffusion films, light concentrating films, and so on that are used in liquid crystal televisions (LCDs), plasma display televisions (PDPs), rear projection televisions (RP-TVs) and others from the viewpoint of excellent mechanical property, dimension stability and transparency thereof, and others. In many cases, a film having a thickness of 50 μm or more is used. When a polyester film is used in the above-mentioned articles or the like, the film is required to have, for example, adhesion to a hard coat layer, adhesion to a prism lens, adhesion to a lenticular lens, or adhesion to an optical diffusion layer. In these layers, ultraviolet (UV) curable resin is generally used in many cases. The film is required to have adhesion to the layers.
In the meantime, in the surface of biaxially oriented polyester films, generally, the crystal thereof is highly oriented; thus, the films have a drawback of being poor in adhesion to various paints, adhesives, inks and others products. A case where the films are used for the above-mentioned optical articles is not exceptional, either. The films are not adhered at all to, for example, a UV curable resin which constitutes a hard coat layer or a prism lens layer. Accordingly, in a working step after the formation of the functional layer, or in actual use of the optical articles, a problem that the functional layer is peeled off from the base film, and other problems are caused. For this reason, methods have been hitherto investigated for giving an easily-adhering property to the surface of a polyester film in various manners. Suggested are, for example, methods of forming an acrylic-modified polyurethane, into a primer layer, on the surface of a film (Japanese Unexamined Patent Publications (Kokai) 1: JP-A-346019 (claims on page 1) and (Kokai): JP-A-2000-229394 (claims on page 1)), a method of forming a copolymerized polyester into a primer layer (Japanese Unexamined Patent Publication (Kokai): JP-A-2001-138465 (claims on page 1)), methods of forming a copolymerized polyester resin and an isocyanate crosslinking agent into a primer layer (Japanese Unexamined Patent Publications (Kokai): JP-A-9-11423 (claims on page 1), JP-A-2002-53687 (claims on page 1) and JP-A-2003-49135 (claims on page 1)), and a method of using a carbodiimide crosslinking agent as a crosslinking agent in a primer layer (Japanese Unexamined Patent Publication (Kokai): JP-A-2001-79994 (claims on page 1)). In the art, carried out are actively, in particular, methods of forming the primer layer by coating, so as to supply an easily-adhering property, in particular, a method (in-line coating method) of subjecting, optionally, a polyester film before the crystal orientation thereof is completed to corona discharge treatment, coating the film with a coating solution containing any one of the above-mentioned resin components, drying the resultant, and subjecting the dried matter to drawing and heating treatment to complete the crystal orientation.
However, the above-mentioned conventional techniques have problems as follows:                About the supply of adhesion, in, e.g., the method of forming an acrylic-modified polyurethane into a primer layer onto the surface of a film or the method of forming a copolymerized polyester into a primer layer, there is easily caused, for example, a problem that the adhesion to a UV curable resin is insufficient or adhesion after the film is stored in a wet heating environment (adhesion after wet heat aging) is not obtained at all. In the method wherein a crosslinking agent is positively used, for example, the method of forming a copolymerized polyester resin and an isocyanate crosslinking agent into a primer layer, or the method of using a carbodiimide crosslinking agent as a crosslinking agent in a primer layer, the effect of improving the adhesion after wet heat aging is recognized; however, in many cases, the adhesion thereof to UV curable resin, in particular, a solvent-free type UV curable resin which constitutes a prism lens layer, or some other resin is not yet sufficient.        About a functional film to which a unique surface shape is given, such as a prism lens layer, a lenticular layer or an optical diffusion layer, UV rays are radiated thereto from the side of a PET film thereon in the production of the film so as to cure the solvent-free type UV curable resin therefor in many cases. In particular, in the case of forming such functional films on both surfaces of the PET film, or in some other case, there remains a serious problem that original adhesion function is not expressed, such as a problem that a layer formed on the PET film is deteriorated by UV rays radiated when the UV curable resin on one of the surfaces is formed into a shape and cured, so that the adhesion to a solvent-free type UV curable resin that will be next formed onto the opposite surface is not obtained. Of course, not only in the case of forming the same UV curable resin on both the surfaces but also in the case of forming, for example, an adhesive agent on the opposite surface, the phenomenon that the easily-adhering layer is deteriorated by UV rays may cause a serious problem against product characteristics, in particular, durability.        
Thus, it could be advantageous to provide a laminate film which is excellent not only in initial adhesion but also in other adhesions, in particular, adhesion after wet heat aging and adhesion after irradiation with UV rays, and further quite excellent in transparency and coating appearance.